The present invention relates to a flexible shaft coupling having two coupling parts connected one with the other via a plurality of flexibly deformable coupling elements distributed about the circumference of the coupling parts.
Flexible shaft couplings of this kind have been generally known in the form of flexible jaw couplings. A jaw coupling of this type includes between an outer coupling part and an inner coupling part a defined number of flexible coupling elements in the form of rubber cushions, that are held in the outer coupling part. The space between neighboring coupling elementsxe2x80x94viewed in circumferential directionxe2x80x94is engaged by jaws of the inner coupling part, that exert a pressure on the rubber cushions when the two coupling parts are rotated one relative to the other. Such a flexible shaft coupling exhibits high torsional rigidity and is particularly well suited for the transmission of high torques.
From DE 36 21 187 A1 there has been known a flexible shaft coupling where a plurality of elastically deformable coupling bodies, each of hollow cylindrical configuration, are distributed in circumferential direction between a radially inner coupling hub and a radially outer coupling flange. The hollow cylindrical coupling bodies are provided on two opposite sides with holding strips molded to their outer jacket, for being introduced in axial direction into corresponding holding grooves provided on the coupling flange and/or the coupling hub. The coupling bodies are thus positioned between the coupling hub and the coupling flange, so that the coupling hub and the coupling flange are connected one with the other through the flexible coupling bodies. Each coupling body is flanked on both sidesxe2x80x94viewed in circumferential directionxe2x80x94by a pair of cams with one cam each, arranged on the coupling flange, pointing radially to the inside and another cam each, arranged on the coupling hub, pointing radially to the outside. The cams are arranged at a distance from the respective coupling body, viewed in circumferential direction, and the cams of the coupling flange are axially spaced from the cams of the coupling hub so that they can move one past the other during relative rotation in circumferential direction. In the presence of low torques, the coupling elements of the flexible shaft coupling are initially subjected to thrust and shear stress until the relative rotation between the coupling hub and the coupling flange proceeds to a degree where the respective cams get into contact with the outer jacket of the coupling bodies. From that point on the coupling bodies are subjected to compressive stress. It is thus possible not only to transfer high torques with high torsional rigidityxe2x80x94as is the case with jaw couplingsxe2x80x94but also to transfer low torques with relatively small torsional rigidity, so that the flexible shaft coupling provides a torsional rigidity adapted to a larger torque range.
Now, it is the object of the present invention to provide a flexible shaft coupling of the before-mentioned kind which enables in a simple way both the transmission of small torques with low torsional rigidity and the transmission of high torques with correspondingly higher torsional rigidity.
This object is achieved by the fact that the coupling elements are positively held in recesses of the one coupling part, that each coupling element comprises a receiving opening that is engaged by a corresponding jaw of the other coupling part, and that the coupling elements comprise at least one cavity, at least on one side of the respective receiving opening for the corresponding jawxe2x80x94viewed in circumferential direction. The solution according to the invention allows a wide torque range to be covered. Specifically, the flexible coupling elements and, thus, the shaft coupling has a soft characteristic due to the fact that the cavities of the coupling elements can be compressed. The cavities reduce the torsional rigidity of the coupling elements due to the fact that cavities neighboring the wall sections of each coupling element are deformed already in the presence of small torques. In a higher torque range, the cavities are compressed to a block so that the flexible coupling elements act in the way of block-shaped elastically deformable coupling elements, which results in a hard characteristic. Thus, once the cavities are compressed, the flexible coupling elements are subjected to compressive stress, in consequence of the resulting block form, so that a hard torque characteristic similar to that of a known flexible jaw coupling is obtained. The soft lower torque range extends preferably over 15% to 20% of the nominal torque range covered by the flexible shaft coupling. The cavities are open either axially or radially, depending on the orientation of the coupling elements, so that in the event of any deformation of the adjoining wall sections no pressure differentials can occur between the interior of the cavity and its environment. The solution according to the invention therefore provides two steps of flexibility of the coupling elements, whereby a two-step flexible shaft coupling is obtained. Depending on the configuration of the cavities and the thickness of the wall sections adjoining the cavities, it is also possible to make the coupling elements deformable in more than two steps until they assume the shape of a closed block, in which case the cavities with the adjoining thin wall sections are the first to be compressed to the shape of a block, while the remaining cavities with correspondingly thicker adjoining wall sections are compressed only thereafter, over an even higher torque range. The soft deformation characteristicxe2x80x94compared with the coupling elements compressed to block shapexe2x80x94results for cavities arranged on both sides of the receiving openings for the corresponding jawsxe2x80x94viewed in circumferential directionxe2x80x94from the fact that the leading cavities in the sense of rotation are compressed whereas the trailing cavities in the sense of rotation are extended. Given the fact that on the one hand the coupling elements are positively held in recesses in the one coupling part and that on the other hand the jaws closely engage the respective receiving openings of the coupling elements, the shaft coupling operates without play over the entire torque range. According to a particularly advantageous feature, the individual elements of the shaft coupling can be simply fitted together in axial direction, when the coupling elements are axially aligned, it being merely necessary to insert the jaws axially into the coupling elements, which are already positioned in the recesses of the other coupling part. This intermateability enables the parts to be assembled blind inside a transmission bell. In addition, the intermateability of the coupling permits shaft displacements to be accommodated in radial, axial and angular direction. Another significant advantage of the solution according to the invention lies in the fact that the shaft coupling requires only little overall space, as the two or more steps of the torque characteristic can be realized with a single sort of coupling element. Advantageously, the one-piece coupling elements are made integrally from an elastic, resilient material, especially from rubber or a rubber substitute. The rubber substitute employed may consist of thermoplastic elastomers, composite materials or similar materials, in addition to the usual substitute materials, such as silicone or the like.
According to a further development of the invention, the cavities are configured as displacement spaces that are open or closed in a radial plane related to the axis of rotation. This allows the deformation characteristic to be additionally influenced.
According to a further development of the invention, at least one cavity is provided in each coupling element on both sidesxe2x80x94viewed in circumferential directionxe2x80x94of the respective receiving opening. This allows the shaft coupling to be operated in both senses of rotation.
According to a further development of the invention, the cavities are configured in each coupling element symmetrically to the receiving opening, viewed in circumferential direction. This enables the coupling to be operated identically in both senses of rotation.
According to a further development of the invention, the cavities exhibit an asymmetrical configuration, depending on the sense of rotation. This makes the coupling operable in only one sense of rotation, the cavities being configured in a way especially adapted to the requirements of that particular sense of rotation.
According to a further development of the invention, the coupling elements are provided with a jacket made from a material with functional properties different from those of the flexibly deformable material of the coupling elements. This further extends the possible range of applications of the coupling. If the jacket is made from a metal or the like, this provides an advantageous support for the soft elastomer. A molded-on jacket further serves to achieve efficient fixing, especially by an interference fit, of the coupling elements in the recessed projections of the coupling flange.
According to a further development of the invention, the closed displacement spaces are part of a damping circuit operating with a damping agent. This makes the coupling elements act additionally as damping members in the circumferential direction.